We have investigated the interaction of lipoproteins with liposomes to form recombinant particles. A number of lipoprotein fractions (VLDL, IDL, LDL, and HDL) all disrupt liposome structure by an essentially irreversible and quasistoichiometric process. In the case of HDL, the major apoprotein, A-I, recombines with dimyristoyl phosphatidyl choline vesicles at 40:1 lipid:protein to form discs approximately 100 A in diameter and 32 A in thickness, with protein on the rim. These structural results were obtained by a combination of neutron scattering, electron microscopy, and column chromatography. With dipalmitoyl phosphatidylcholine, A-I also forms what we term "vesicular recombinant" particles in a process which may relate to physiological mechanisms by which proteins are assembled into membranes and lipoproteins. To study this process we have developed a technique called "phase transition release" (PTR), which is also being applied to study incorporation of tubulin into membranes.